1. Field of the Invention
The present invention relates to a constant-speed running controller for vehicle equipped with an engine.
2. Description of the Related Art
Recently, it has become known to provide a vehicle equipped with an electronic throttle controller referred to as DBW (drive by wire) for electrically controlling the opening of a throttle valve without mechanically associating the opening of the throttle valve with an accelerator pedal operation. In the electronic throttle controller, a target opening is set for the throttle valve based on vehicle driving conditions, such as the amount of accelerator pedal operation, and the throttle valve is electrically controlled through an actuator to provide the target opening.
A vehicle equipped with the electronic throttle controller has the throttle opening characteristic stored as a data table indicative of a throttle opening for the amount of accelerator pedal operation. Also, the throttle opening characteristics are provided individually for respective operating conditions such as an acceleration to select a throttle opening characteristic in accordance with actually detected operating conditions for use in controlling the throttle.
When a vehicle equipped with such an electronic throttle controller has a constant-speed running controller for operating the vehicle at a constant speed, the throttle valve opening is controlled in accordance with a change in running load such as a slope to maintain the constant-speed running or operation even if the accelerator pedal is not actuated during the constant-speed running control. Also, when the driver""s intention for acceleration is detected from actuation of accelerator pedal during the constant-speed running control, a temporary transition to an accelerating operation is made.
As the control for constant-speed running, it is known that there are apparatuses which employ a method of controlling the opening of a throttle valve in accordance with the vehicle speed or a method of controlling the transmission stage (including a lock-up clutch) of an automatic transmission together with the opening of a throttle valve. Also, Laid-open Japanese Patent Application No. 10-306871 discloses a constant-speed running controller which calculates a pseudo-acceleration opening in accordance with a difference between an actual vehicle speed and a target speed to control the opening of a throttle valve in accordance with the pseudo-acceleration opening in a constant-speed running mode.
FIG. 1 shows an example of changes in vehicle speed, running load, throttle valve opening, amount of accelerator pedal operation, and transmission stage of an automatic transmission in the constant-speed running mode, when using a constant-speed running controller for controlling the throttle valve opening in accordance with the vehicle speed. In FIG. 1, when the running load increases due to a slope in a constant-speed running mode, the vehicle speed decreases from a target speed (broken line), and the throttle valve opening is controlled to increase from a target opening. This causes the speed to increase back to the target speed. Conversely, when the running load decreases, the vehicle speed increases from the target speed, and the throttle valve opening is controlled to decrease from the target opening in response thereto. This causes the speed to decrease back to the target speed. The transmission stage of the automatic transmission is maintained, for example, at a fourth speed. When the accelerator pedal is depressed by the driver for acceleration at a time T in the constant-speed running mode, if the amount of accelerator pedal depression (accelerating pedal opening) exceeds the target opening of the throttle valve opening, the throttle valve opening is controlled to increase from the target opening in response to the operation of the accelerator pedal before proceeding to an accelerating operation.
However, in the conventional constant-speed running controller, since the actual opening of the throttle valve does not change until the accelerating pedal operation exceeds the target opening of the throttle valve opening even if the accelerator pedal is depressed by the driver for acceleration at the time T in the constant-speed running mode, a so-called dead zone occurs, resulting in a problem that good drivability is not provided.
FIG. 2 shows an example of changes in vehicle speed, running load, throttle valve opening, amount of accelerator pedal operation, and transmission stage of an automatic transmission in the constant-speed running mode, when using a constant-speed running controller for controlling the transmission stage of an automatic transmission together with the throttle valve opening. In FIG. 2, when the running load increases due to a slope in the constant-speed running mode, the vehicle speed decreases from a target speed (broken line), and the throttle valve opening is controlled to increase from a target opening in response thereto. The automatic transmission is also shifted down due to the increased throttle valve opening. This causes the speed to increase back to the target speed. Conversely, when the running load decreases, the running speed increases from the target speed, the throttle valve opening is controlled to decrease from the target opening in response thereto, and the automatic transmission is shifted up due to the decreased throttle valve opening. This causes the speed to decrease back to the target speed. When the accelerator pedal is operated by the driver for acceleration at a time T in the constant-speed running mode, the throttle valve opening is immediately controlled to increase from the target opening during the constant speed running in accordance with the amount of accelerator pedal operation to proceed to an accelerating operation.
The constant-speed running controller shown in FIG. 2 can immediately proceed to the accelerating operation even if the accelerator pedal is operated for acceleration in the constant-speed running mode. However, since the target opening of the throttle valve is set higher than a throttle valve opening corresponding to the degree of accelerator pedal operation of zero, the transmission stage of the automatic transmission shifts down to cause shift hunting from a fourth speed to a second speed as shown in FIG. 2. Otherwise, the lock-up of the automatic transmission turns off in an unexpected situation, causing another problem of vehicle shock.
FIG. 3 shows an example of changes in vehicle speed, running load during a constant-speed running mode period (in a period in which a cruise switch is on), throttle valve opening, accelerator pedal operation, pseudo-throttle valve opening, and transmission stage of an automatic transmission when using a constant-speed running controller shown in the above-mentioned Laid-open Japanese Patent Application No. 10-306871.
Since the constant speed running controller calculates a pseudo-acceleration opening in accordance with a difference between an actual vehicle speed and a target speed to control the throttle valve opening in accordance with the pseudo-acceleration opening in the constant-speed running mode, as described above, there is a problem that the throttle valve opening is discontinuous immediately after starting or ending the constant-speed running mode so as to cause an unexpected shift-up or shift-down of the automatic transmission. There is also another problem that since the throttle valve opening is eventually controlled in accordance with the difference in vehicle speed, even if the running load increases due to a slope in the constant-speed running mode, the automatic transmission has a delayed downshift, causing the vehicle speed to substantially decrease from the target vehicle speed.
It is therefore an object of the present invention to provide a constant-speed running controller for a vehicle which is capable of improving the follow-up characteristic to a target vehicle speed and the drivability for operation of the accelerator pedal in a constant-speed running mode.
A constant-speed running controller of the present invention is a constant-speed running controller for a vehicle-equipped with an engine, comprising an automatic transmission disposed in a driving power transmission system from the engine to wheels, having a plurality of transmission stages; throttle valve opening setting means for setting a target throttle opening of a throttle valve such that the speed of the vehicle is at a target vehicle speed; accelerating pedal opening detecting means for detecting an amount or degree of accelerator pedal operation as an accelerating pedal opening; adding means for adding the target throttle opening set by the throttle valve opening setting means and the accelerating pedal opening detected by the accelerating pedal opening detecting means to generate an opening signal as an addition result; throttle valve driving means for driving the throttle valve based on the output opening signal of the adding means; and transmission stage control means for controlling the transmission stage of the automatic transmission in accordance with the output opening signal of the adding means.
According to the constant-speed running controller of the present invention in the foregoing configuration, even if the vehicle speed decreases or increases from a target vehicle speed due to a change in running load in the constant-speed running mode, a target throttle opening set by the throttle valve opening setting means in response to the change is supplied to the throttle valve driving means and to the transmission stage control means as an opening signal of the adding means, the throttle valve opening and the transmission stage of the automatic transmission are adjusted to immediately return to the target vehicle speed. Also, since an accelerating pedal opening detected by the accelerating pedal opening detecting means is added to the target throttle opening set by the throttle valve opening setting means in response to an operation on the accelerator pedal by the driver in the constant-speed running mode, and an opening signal as the addition result is supplied to the throttle valve driving means, the throttle valve opening can be increased to immediately accelerate the vehicle.